题目

风洞实验室中可以产生水平向右的、大小可调节的风力，现将一套有小球的细直杆放入风洞实验室，小球孔径略大于细杆直径，杆足够长，如图所示，小球的质量为1kg，球与杆间的滑动摩擦因数为0.5．（取g=10m/s2） （1） 当杆在水平方向上固定时（如图虚线所示），调节风力的大小，使风对小球的力大小恒为4N，求此时小球受到的摩擦力f1的大小． （2） 若调节细杆使杆与水平方向间夹角θ为37°并固定（如图实线所示），调节风力的大小，使    “Imagine you are walking along the road. Suddenly you fall over and all the passers-by burst into laughter. You feel very  16  and think the world is laughing at you. But in fact, five minutes later, they have  17  it ever happened.” The other day when I came across these words in an article, I didn’t agree with the  18 .    The author thinks the best thing to do in this kind of  19  is to pretend nothing has happened, and so avoid  20  trouble.    I admit that we should keep  21  because “Your tears will only remind others of what happened, while your  22  can let them forget it.” But this is far from satisfactory. We should do  23  to make things better.    I used to be a(n)  24  girl and not very good at maths. Our new maths teacher asked me a question and I still remember how I hung my head in  25  when I couldn’t answer it.    “If you don’t know the answer, just tell me.” the teacher said, “If you don’t, how can I know  26  you know the answer or not?” All of my classmates burst into laughter. My face turned red but the teacher  27  me to go to the blackboard and  28  what I knew. If I had  29  the words in the article, I would have given up. But I tried my best. And to everyone’s  30 , I succeeded! The teacher smiled and said, “Well done! I  31  you could do it!”    Since then, I have become active in maths as  32  as in other subjects. I used to think doing maths exercises was a waste of time. But now, I know  33  I do can make things better. Everyone is the  34  of his own fate.    If we make mistakes, we should take on an active  35 . Laugh, and the world laughs with you; weep, and you weep alone.16. A. nervous   B. excited    C. afraid   D. embarrassed17. A. realized     B. recognized       C. forgotten       D. remembered18. A. speaker     B. reader           C. author         D. announcer19. A. environment  B. surrounding      C. condition      D. situation20. A. ordinary   B. extra            C. common       D. usual21. A. confident    B. smart   C. calm          D. strong22. A. smile       B. worry           C. courage        D. satisfaction23. A. anything     B. something       C. nothing        D. everything,24. A. shy     B. energetic C. happy         D. clever25. A. joy        B. pride            C. shame         D. surprise26. A. what      B. that      C. when          D. whether27. A. forced      B. invited    C. asked   D. pushed28. A. bring up      B. put down       C. think about    D. show off29. A. obeyed  B. suspected        C. rejected        D. understood30. A. expectation   B. disappointment   C. surprise        D. delight31. A. hoped   B. knew           C. doubted        D. regretted32. A. long      B. far    C. soon          D. well33. A.. whoever    B. whenever        C. wherever       D. whatever34.i A. architect   B. owner          C. host   D. inspector35. A. position    B. attitude          C. value          D. response